There has been an increased recent demand for styrene and other resins of reduced flammability. Various methods have been proposed to make styrene resins, and poly(para-methylstyrene) resin, including high-impact polystyrene, high-impact poly(para-methylstyrene), styrene-acrylonitrile-butadiene copolymers, styrene-methyl methacrylate-butadiene copolymers, and the like, less flammable. For example styrene resins and poly(para-methylstyrene) resins having a reduced tendency to ignite and propagate flame in the absence of an external heat source have been prepared by adding an organic halide and an inorganic flame retardant, such as antimony trioxide.
Organic halides are very effective in providing the polymers with a reduced tendency to ignite and burn in the absence of an external heat source, but have a tendency to make the polymers drip while they are burning, and, in order to achieve flame retarded compositions in the range of V-1 to V-0 provided under Subject 94 by Underwriter's Laboratories, Inc. (hereinafter referred to as UL-94), a large amount of halide must be added. The use of antimony compounds in combination with the halides is known to be effective in overcoming the dripping problem. However, even with the addition of the antimony compounds, the polymers tend to drip as the thickness of polymer moldings becomes smaller, and it is very difficult to bring the polymers to conform to the range of V-1 to V-0 under UL 94. In accordance with this invention, octahalogenated biphthalyl is used as the organic halide in conjunction with an inorganic flame retardant such as antimony trioxide to achieve excellent flame-retardancy.
The tests employed herein to demonstrate suppressed ignition properties and burning accurately demonstrate the ignition or burning characteristics of the polymers when exposed to small scale ignition sources according to the standards specified. It is well recognized by those skilled in the art and it should be clearly understood that all known organic polymers will burn when subjected to a sufficiently intense heat source whether or not they contain a fire-retardant additive. "To drip" or "dripping" referred to hereinafter, according to the vertical burning tests under UL-94, means to drip particles from a specimen during the application of a test flame or after the removal of the flame. Failure to achieve a V-1 or V-0 rating results when the dripping particles ignite a piece of cotton held under the specimen, regardless of whether or not the particles were flaming.